1. Field of the Invention
Applicant's invention relates to an apparatus and method for metering and atomizing liquids in small quantities and at high rates. This invention is particularly applicable to the metering and delivery of fuel to an internal combustion engine, however, it is readily appreciated that there are other applications in which the metering and atomization of a liquid is desired.
2. Summary of Prior Art
The delivery of fuel to internal combustion engines has historically been accomplished by carburetors. The wick carburetor and the surface carburetor were used between 1848 and 1900. These devices use the evaporation of liquid fuel to form the combustible mixture.
Except for these early attempts, engine fuel has been mechanically dispersed using either jets located in a venturi tube, such as in a carburetor or by forcing the fuel through a nozzle as in a fuel injector.
In an engine, the fuel must be sufficiently atomized so that the fuel will burn in a relatively short period of time. In an Otto cycle engine, combustion of the fuel and air begins slightly before the piston reaches top dead center (TDC), continues throughout much of the power stroke, and should optimally be completed before the piston reaches the bottom of its stroke because only during the expansion of the burning gas is energy transferred to the piston.
A typical carburetor provides a degree of self-regulation of the air-fuel ratio. As the throttle is opened, more air is passed through the intake manifold, through the venturi, and then through the engine's combustion chamber. As more air is admitted, the velocity of the air through the carburetor venturi increases which, in turn, decreases the air pressure at the carburetor jets. This decreased pressure pulls fuel from the jets into the air stream. The amount of fuel expelled is determined by the difference in pressure between the fuel at the carburetor jets in the venturi and atmospheric pressure.
The optimal combustion of fuel in an internal combustion engine involves several factors. First, the proper ratios of fuel and air are necessary to prevent damage to the engine and to minimize exhaust emissions. For a gasoline burning internal combustion engine the stoichiometric ratio is 14.7 times as much air as gasoline by weight.
A second factor is the load on the engine. For light load, part throttle operation, an air:fuel ratio as low as 16.1:1 would be adequate, but for a full load such as full throttle acceleration, an air:fuel ratio of 12:1 may be required. Other factors to be considered when determining the proper air:fuel ratio include: engine speed, ambient and engine temperature, and the specific density of the fuel.
A typical carburetor provides a relatively good degree of self-regulation over the air and fuel mixture because of the inherent design. The float maintains a constant head of fuel relative to the carburetor jets. As fuel is consumed, the fuel level in the float chamber drops which causes the float to pivot downward on the float arm which pulls the needle valve from its seat. This allows more fuel to fill the float chamber or float bowl. The carburetor jets are located in the venturi and are fed with fuel from the float chamber. The float bowl is vented to the atmosphere so the total differential pressure across the jets is proportional to the height of the fuel above the jets plus the differential pressure between atmospheric and the manifold pressure at the jets. Manifold pressure at the jets is a function of manifold pressure and the velocity of the air through the venturi. Thus, as the throttle is opened the air flow increases, the air pressure in the venturi drops, and more fuel is pulled from the float bowl into the air stream.
The carburetor's simple design and ability to provide an air:fuel fixture within 5% of the ideal mixture made the carburetor the accepted fuel delivery and mixing device in the early evolution of internal combustion engines. However, current demands on internal combustion engines of fuel economy and minimized exhaust emissions demand more than the approximation of the proper air:fuel mixture.
Automotive internal combustion engines now use engine control computers to measure the intake air temperature, coolant temperature, air pressure, engine speed and load, and throttle position. The control computer can then calculate the correct air:fuel mixture and adjust the fuel delivery system appropriately.
Fuel injection was developed as an alternate mechanical system used to mix and to deliver fuel and air to internal combustion engines. Fuel injection was first widely applied to the diesel engines where the carburetor did not furnish sufficient atomization of the fuel. Diesel fuel is heavier and less volatile than gasoline, thus very high pressure was needed to properly atomize and meter the fuel.
The first automobile gasoline fuel injectors were direct, mechanical fuel injectors developed by Bosch and Mercedes-Benz in the early 1950's. These fuel injectors pumped the fuel either directly into the cylinder or into the intake manifold. High pressure injection pumps, directly driven from the engine, discharged fuel through rigid tubing to the nozzle. The nozzle discharge pressures were about 1500 psi to properly atomize the fuel. The fuel pressure overcame a spring loaded valve in the injector body which eliminated the need for a return fuel line.
In the late 1950's Mercedes-Benz began the development of port injection which could use lower fuel pressures, as the injection did not have to overcome combustion chamber pressures. This was first used in the 1957 Mercedes-Benz 300d and port-type injectors have been universal since then.
A common problem in pulsed or intermittent fuel injectors is that the fuel may "blob" on the nozzle rather than being atomized. This is generally caused by either a slow pressure rise or the loss of pressure in the fuel lines between the nozzle, and the liquid forms a "blob" or drop on the intake manifold side of the injector. This excess fuel is then carried into the combustion chamber as a drop too large to undergo complete combustion under the constraints of engine operating conditions. Incomplete combustion will contribute both to wasted fuel and to increased emissions.
An early electronic fuel injection system, is known wherein a pressurized fuel supply (typically 20 to 100 psi) is delivered to each injector from a fuel pump, which supplies the mechanical energy required for atomization, stored as compression of the fuel. The injector body contains a solenoid, which, when energized, allows fuel to pass into the nozzle. Although this design has been improved, particularly the controlling electronics, the basic operation has stayed the same.
Gianini in U.S. Pat. No. 3,610,213 designed a fuel injector trying to minimize inconsistent air:fuel ratios, pulsations caused by the high frequency of breaks in the fuel stream (caused by the cycling of the injectors), and improper fuel storage in the intake manifold. Gianini's invention consists of a fuel injection system having a separate fuel source, an injector having a fuel reservoir of a size at least as great as the volume of fuel to be injected into the cylinder, a mechanical pump to supply fuel from the fuel source to the injector reservoir, an air source, and a separate pump to supply the air to the injector to atomize the fuel in the reservoir.
U.S. Pat. No. 4,429,674 issued to Lubbing teaches a multi-cylinder internal combustion engine having a fuel source, an air source, premixing of the fuel and air in the injection nozzle, a discharge orifice continuously discharging the premixed air and fuel to a common fuel supply chamber, and a separate air intake system using air to supply the premixed air and fuel to the engine cylinders. The use of air is primarily for transporting the premixed air and fuel mixture. The air does not assist in the generation or metering of the air-fuel mixture for combustion. The initial fuel-air mixture is generated using the current technology, that is a conventional nozzle.
Another fuel injector design is disclosed by Sarich in U.S. Pat. No. 4,462,776. Sarich teaches a method and apparatus for delivering metered quantities of liquid wherein the liquid is circulated through a metering chamber, filling the chamber with the liquid, closing the liquid circulation ports when the metering chamber is full, opening a gas inlet port and a discharge port, and admitting gas under pressure through the gas inlet port into the metering chamber and expelling the liquid from the metering chamber through the discharge port. Once the liquid is expelled, the gas inlet port and the discharge port are closed and the fuel is again circulated through the metering chamber. The amount of liquid in the metering chamber can be regulated only by moving the gas inlet port mechanism so as to define a larger or smaller cavity.
A fuel injection system with a leakage collection is disclosed in McKay, U.S. Pat. No. 4,554,945. McKay consists of a metering chamber, a gas supply chamber, a metering member, and a leakage collection chamber. The metering member movable extends into the metering chamber to meter the fuel. Gas carried by the metering member displaces the fuel in the metering chamber. Any gas or fuel leakage collects in the leakage collection chamber and is returned to its appropriate chamber.
An attempt to minimize cycle to cycle variation in fuel delivery caused by the build up of residual fuel is disclosed by Smith, U.S. Pat. No. 4,712,524. Smith believes that average thickness of the residual fuel film on the wall of the fuel delivery tube between the metering device and the engine increases as the metered quantity of fuel per delivery increases, when a fixed amount of air is used to convey the fuel through the delivery tube. To resolve this problem, Smith teaches a method of delivering fuel to an internal combustion engine comprising the delivering of individual metered quantities of fuel into a conduit by an individual air pulse, and establishing a secondary gas flow in the conduit to sweep the conduit clean. The secondary gas flow would only occur for part of the time interval between respective air pulses to deliver the metered quantities of fuel along the conduit. The individual air pulses do not meter the fuel as the metering of the fuel is accomplished using standard metering devices.
Electronic fuel injectors are replacing entirely mechanical injectors because electronic fuel injectors allow greater monitoring of relevant factors and subsequent metering of the fuel and air mixture for combustion. Development of the electronic fuel injectors has concentrated primarily on the electronics associated with the electronic fuel injectors allowing monitoring of numerous conditions such as: intake air mass, air pressure, air temperature, coolant temperature, oil temperature, engine load, throttle position, crankshaft position, engine revolutions per minute, and exhaust gas composition. Complete computerization of the fuel injection and spark ignition have led to greater fuel efficiency, power, and reduced emissions.
The current fuel injection systems suffer from several problems, namely they are complex, fragile, and require excessive maintenance than is desirable. Fuel metering is generally accomplished by metering chambers, requiring complex apparatus to vary the volume of the charge of fuel. Therefore, a practical and economical solution is needed for these problems.